U.S. patent number 5,258,340 [Application Number 07/656,306] was granted by the patent office on 1993-11-02 for mixed transition metal oxide catalysts for conversion of carbon monoxide and method for producing the catalysts.
This patent grant is currently assigned to Philip Morris Incorporated. Invention is credited to Robert L. Augustine, Setrak Tanielyan.
United States Patent |
5,258,340 |
Augustine , et al. |
November 2, 1993 |
Mixed transition metal oxide catalysts for conversion of carbon
monoxide and method for producing the catalysts
Abstract
This invention relates to improved catalysts for the oxidation
of carbon monoxide and methods of preparing these catalysts. The
catalysts of this invention are prepared using a sequential
precipitation process which generates catalysts that contain
substantially layered metal oxides, both supported and unsupported,
and, in some embodiments of the invention, a noble metal or mixture
of noble metals layered on the metal oxides. These catalysts are
particularly useful in smoking articles.
Inventors: |
Augustine; Robert L.
(Livingston, NJ), Tanielyan; Setrak (South Orange, NJ) |
Assignee: |
Philip Morris Incorporated (New
York, NY)
|
Family
ID: |
24632499 |
Appl.
No.: |
07/656,306 |
Filed: |
February 15, 1991 |
Current U.S.
Class: |
502/60; 502/183;
502/338; 502/337; 502/331; 502/330; 502/329; 502/326; 502/325;
502/313; 502/244; 502/184; 502/242; 502/185 |
Current CPC
Class: |
B01J
37/16 (20130101); B01J 37/0244 (20130101); B01J
37/0221 (20130101); B01J 23/835 (20130101); B01J
23/8966 (20130101); B01J 37/031 (20130101); B01J
23/8926 (20130101); B01D 53/864 (20130101); B01J
21/08 (20130101) |
Current International
Class: |
B01J
37/00 (20060101); B01J 37/03 (20060101); B01D
53/86 (20060101); B01J 023/72 (); B01J 023/80 ();
B01J 023/82 (); B01J 023/84 () |
Field of
Search: |
;502/242,244,325,326,338,60,183,184,185,329,330,331,337 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
0395956 |
|
Nov 1990 |
|
EP |
|
1315850 |
|
May 1973 |
|
JP |
|
36387 |
|
Aug 1973 |
|
JP |
|
139684 |
|
Nov 1977 |
|
JP |
|
112793 |
|
Sep 1979 |
|
JP |
|
0130835 |
|
Jan 1985 |
|
JP |
|
238148 |
|
Nov 1985 |
|
JP |
|
227842 |
|
Oct 1986 |
|
JP |
|
252908 |
|
Oct 1988 |
|
JP |
|
Other References
M Haruta, N. Yamada, T. Kobayashi, and S. Iijima, "Gold Catalysts
Prepared by Coprecipitation for Low-Temperature Oxidation of
Hydrogen and of Carbon Monoxide," Journal of Catalysis, 115, pp.
301-309 (1989). .
M. Haruta, T. Kobayashi, S. Iijima, and F. Delannay, "Ultrafine
Gold Particles Immobilized with Oxides of Fe, Co, or Ni for the
Catalytic Oxidation of Carbon Monoxide at -70.degree. C.,"
Proceedings-International Congress on Catalysts, 3, pp. 1206-1213
(1988). .
M. Haruta, T. Kobayashi, H. Sano, and N. Yamada, "Novel Gold
Catalysts for the Oxidation of Carbon Monoxide at a Temperature far
Below 0.degree. C.," Chemistry Letters, 2, pp. 405-408 (1987).
.
M. Haruta, Y. Souma, and H. Sano, "Catalytic Combustion of
Hydrogen: Development of Oxide Catalysts and Experimental Tests for
Combustor Design," Advanced Hydrogen Energy, 2, pp. 1135-1147
(1981). .
G. C. Bond and D. E. Webster, "Catalytic Activity of Reduced Noble
Metal-Base Metal Mixed Oxides," Chemistry and Industry, pp. 878-879
(1967)..
|
Primary Examiner: Shine; W. J.
Attorney, Agent or Firm: Loring; Denise L.
Claims
We claim:
1. An oxidation catalyst for use in low temperature oxidation of
carbon monoxide comprising a plurality of metal oxide layers,
wherein at least one of said layers comprises cobalt(II,III)oxide
and at least another one of said layers comprises a metal oxide
selected from the group consisting of the oxides of iron, nickel,
copper, zinc, molybdenum, tungsten, and tin.
2. The catalyst of claim 1, wherein the catalyst consists of two
metal oxide layers and the ratio of weight of the second metal
oxide to the weight of the first metal oxide is from about 1:50 to
about 1:4.
3. The catalyst of claim 1, wherein the catalyst consists of two
metal oxide layers and the ratio of weight of the second metal
oxide to the weight of the first metal oxide is form about 2:50 to
about 1:10.
4. A layered metal oxide catalyst for use in low temperature
oxidation of carbon monoxide comprising a layer of
cobalt(II,III)oxide and a layer of tin oxide.
5. The catalyst of claim 1, further comprising one or more noble
metals, the noble metal or mixture being layered upon the other
metal oxide layer.
6. The catalyst of claim 5, wherein the ratio of the weight of the
noble metals to the weight of the metal oxides is from about 0.1%
to about 5.0%.
7. The catalyst of claim 5, wherein the ratio of the weight of the
noble metals to the weight of the metal oxides is from about 0.1%
to about 1.0%.
8. The catalyst of claim 5, wherein the noble metal is selected
from the group consisting of gold, silver, platinum, palladium,
rhodium, ruthenium and iridium, and mixtures thereof.
9. The catalyst of claim 1 or 5, further comprising a support
material upon which the first metal oxide is layered.
10. The catalyst of claim 9, wherein the support material is
selected from the group consisting of a ceramic, a zeolite, porous
carbon, porous paper, and a metal mesh.
11. A layered metal oxide catalyst for use in oxidizing carbon
monoxide comprising a support material, two metal oxide layers and
an outer noble metal layer, wherein the support material is silicon
dioxide, the first metal oxide layer is cobalt(II,III)oxide, the
second metal oxide layer is tin oxide, and the noble metal is
selected from the group consisting of gold, platinum and mixtures
thereof.
12. A layered metal oxide catalyst for use in oxidizing carbon
monoxide comprising a support material, two metal oxide layers and
an outer noble metal layer, wherein the support material is silicon
dioxide, the first metal oxide layer is cobalt(II,III)oxide, the
second metal oxide is copper oxide, and the noble metal comprises
platinum and rhodium.
13. Method for producing a layered metal oxide catalyst for use in
oxidizing carbon monoxide comprising the steps of:
(a) adding an aqueous solution of a salt of a first metal to an
aqueous solution of a base;
(b) adding to the suspension of step (a) an aqueous solution of a
salt of a second metal;
(c) isolating the precipitate resulting from step (b); and
(d) heating the precipitate, wherein the metal oxides are selected
from the group consisting of the oxides of iron, cobalt, nickel,
copper, zinc, molybdenum, tungsten, and tin.
14. The method of claim 13, wherein in step (a) the base solution
is added to the salt of the first metal oxide.
15. The method of claim 13 or 14, wherein the salt of the first
metal is selected from the group consisting of cobalt(II)nitrate
and iron(III)nitrate and the salt of the second metal is selected
from the group consisting of cobalt(II)nitrate and tin(II)chloride,
wherein the second metal salt is different from the first metal
salt.
16. The method of claim 13 or 14, wherein the base is selected from
the group consisting of sodium bicarbonate, sodium hydroxide,
potassium carbonate and lithium hydroxide.
17. The method of claim 13 or 14, wherein a suspension of a support
is first added to the aqueous solution of the base.
18. The method of claim 17, wherein the support is selected from
the group consisting of a ceramic, a zeolite, porous carbon, porous
paper, and a metal mesh.
19. The method of claim 13 or 14, comprising the additional step of
isolating the precipitate resulting from step (a) and adding it to
the solution of step (b).
20. The method of claim 13 or 14, wherein the precipitate is heated
to a temperature between about 95.degree. C. and about 500.degree.
C.
21. The method of claim 13 or 14, wherein the precipitate is heated
to a temperature between about 300.degree. C. and about 400.degree.
C.
22. The method of claim 13 or 14, wherein the precipitate is heated
for a period of between about 1 hour and about 12 hours.
23. A method for producing a layered metal oxide catalyst for use
in oxidizing carbon monoxide comprising a noble metal layered upon
a second metal oxide which is layered upon a first metal oxide,
comprising the steps of:
(a) adding an aqueous solution of a salt of a first metal to an
aqueous solution of a base;
(b) adding to the suspension of step (a) an aqueous solution of a
salt of a second metal;
(c) adding an aqueous solution of formaldehyde;
(d) adding an aqueous solution of a salt of a noble metal;
(e) isolating the precipitate resulting from step (d); and
(f) heating the precipitate,
wherein the metal oxide are selected from the group consisting of
iron, cobalt, nickel, copper, zinc, molybdenum, tungsten, and tin,
and wherein the noble metal is selected from the group consisting
of gold, silver, platinum, palladium, rhodium, ruthenium and
iridium, and mixtures thereof.
24. The method of claim 23, wherein in step (a) the base solution
is added to the salt of the first metal oxide.
25. The method of claim 23 or 24, wherein the salt of the first
metal is selected from the group consisting of cobalt(II)nitrate
and iron(III)nitrate and the salt of the second metal is selected
from the group consisting of cobalt(II)nitrate and tin(II)chloride,
wherein the second metal salt is different from the first metal
salt.
26. The method of claim 23 or 24, wherein the base is selected from
the group consisting of sodium bicarbonate, sodium hydroxide,
potassium carbonate and lithium hydroxide.
27. The method of claim 23 or 24, wherein a suspension of a support
is first added to the aqueous solution of the base.
28. The method of claim 27, wherein the support is selected from
the group consisting of a ceramic, a zeolite, porous carbon, porous
paper and a metal mesh.
29. The method of claim 23 or 24, comprising the additional step of
isolating the precipitate resulting from step (a) and adding it to
the solution of step (b).
30. The method of claim 23 or 24, wherein the precipitate is heated
to a temperature between 95.degree. C. and 500.degree. C.
31. The method of claim 23 or 24, wherein the precipitate is heated
to a temperature between 300.degree. C. and 400.degree. C.
32. The method of claim 23 or 24, wherein the precipitate is heated
for a period of between about 1 hour and about 12 hours.
33. An oxidation catalyst for use in a smoking article comprising a
plurality of metal oxide layers, wherein at least one of said
layers comprises cobalt(II,III)oxide and at least another one of
said layers comprises a metal oxide selected from the group
consisting o the oxides of iron, nickel, copper, zinc, molybdenum,
tungsten, and tin.
34. A layered metal oxide catalyst for use in a smoking article
comprising a support material, two metal oxide layers and an outer
noble metal layer, wherein the support material is silicon dioxide,
the first metal oxide layer is cobalt(II,III)oxide, the second
metal oxide layer is tin oxide, and the noble metal is selected
from the group consisting of gold, platinum and mixtures
thereof.
35. A layered metal oxide catalyst for use in a smoking article
comprising a support material, two metal oxide layers and an outer
noble metal layer, wherein the support material is silicon dioxide,
the first metal oxide layer is cobalt(II,III)oxide, the second
metal oxide layer is copper oxide, and the noble metal comprises
platinum and rhodium.
36. A layered metal oxide catalyst for use in low temperature
oxidation of carbon monoxide made by the method comprising the
steps of:
(a) adding an aqueous solution of a salt of a first metal to an
aqueous solution of a base;
(b) adding to the suspension of step (a) an aqueous solution of a
salt of a second metal;
(c) isolating the precipitate resulting from step (b);
(d) heating the precipitate, wherein the metal oxides are selected
from the group consisting of the oxides of iron, cobalt, nickel,
copper, zinc, molybdenum, tungsten, and tin.
37. A layered metal oxide catalyst for use in low temperature
oxidation of carbon monoxide comprising a noble metal layered upon
a second metal oxide which is layered upon a first metal oxide made
by the method comprising the steps of:
(a) adding an aqueous solution of a salt of a first metal to an
aqueous solution of a base;
(b) adding to the suspension of step (a) an aqueous solution of a
salt of a second metal;
(c) adding an aqueous solution of formaldehyde;
(d) adding an aqueous solution of a salt of a noble metal;
(e) isolating the precipitate resulting from step (d); and
(f) heating the precipitate,
wherein the metal oxides are selected from the group consisting of
the oxides of iron, cobalt, nickel, copper, zinc, molybdenum,
tungsten, and tin, and wherein the noble metal is selected from the
group consisting of gold, silver, platinum, palladium, rhodium,
ruthenium, osmium and iridium, and mixtures thereof.
Description
BACKGROUND OF THE INVENTION
This invention relates to improved catalysts for the oxidation of
carbon monoxide and methods of preparing these catalysts. The
catalysts of this invention convert carbon monoxide, produced by
the combustion of carbonaceous heat sources, to a benign substance
such as carbon dioxide. The catalysts and methods of this invention
are particularly suitable for use in a smoking article such as that
described in copending U.S. patent application Ser. No. 223,153,
filed on Jul. 22, 1988, now U.S. Pat. No. 4,991,606, (PM-1322) and
commonly assigned herewith.
The catalysts of this invention comprise mixed transition metal
oxide catalysts and catalyst supports. According to the methods of
this invention, the catalysts are prepared using a sequential
precipitation process which generates catalysts that contain
substantially layered metal oxides, and, in some embodiments, a
noble metal or mixtures of noble metals layered on the metal
oxides.
There have been previous attempts to provide catalysts containing
metal oxides and mixed metal oxides alone and in combination with
noble metals or their oxides for the oxidation of carbon monoxide
to carbon dioxide. There have also have been previous attempts to
provide methods for the manufacture of such catalysts. These
attempts have not produced catalysts having all of the advantages
of the catalysts of the present invention.
For example, Callahan et al. U.S. Pat. No. 3,546,138 refers to
oxidation catalysts that consist of a base catalyst containing the
mixed oxides of antimony and iron, on a silica carrier, formed by
coprecipitation. The formation of these catalysts is facilitated by
a metal oxide promoter, which is incorporated into the base
catalyst by coprecipitation or impregnation.
Haruta et al. U.S. Pat. No. 4,698,324 refers to a method for the
manufacture of a composite catalyst having gold or a mixture of
gold and an oxide of chromium, manganese, iron, cobalt, nickel, or
copper, which is deposited on a carrier by coprecipitation. The
method requires that urea and/or acetamide be used as a precipitant
to facilitate the deposit of the gold/metal oxide mixture on a
support in a single step reaction.
Haruta et al., Journal of Catalysis, 115, pp. 301-09 (1989), Haruta
et al., Proceedings--International Congress on Catalysts, 3, pp.
1206-1313 (1988), and Haruta et al., Chemistry Letters, 2, pp.
405-408 (1987), refer to catalysts containing gold in combination
with a single transition metal oxide that are prepared using a
coprecipitation method.
Haruta, et al., Advanced Hydrogen Energy, 2, pp. 1135-47 (1981),
refers to mixed transition metal oxide catalysts used in the
catalytic combustion of hydrogen.
Bond et al., Chemistry and Industry, pp. 878-79 (1967), refers to
mixed noble metal oxides for use in hydrogenation reactions. The
mixed noble metal oxides contain platinum and either iron, cobalt,
nickel or copper, or palladium and either cobalt or nickel.
Bond et al. United Kingdom patent 1,134,111 describes homogeneous
catalyst mixtures comprising a platinum group metal oxide and a
base metal oxide prepared by the fusion of the mixed salts to give
the mixed oxides.
European patent application 0 130 835 describes composite mixed
metal oxide catalysts of lanthanum, neodymium or praseodymium, or
mixtures thereof, supported by aluminum oxide, prepared by a
coprecipitation or an impregnation method.
Japanese patent publication no. Sho 61/1986-227842 refers to carbon
monoxide removing catalysts that are all based on the presence of
manganese dioxide and palladium. These catalysts achieve less
carbon monoxide oxidation than the catalysts of the present
invention.
Japanese patent publication no. Sho 50/1975-36387 refers to
hopcalite catalysts consisting of manganese or manganese oxide that
are prepared using a coprecipitation method.
Japanese patent publication no. Sho 52/1977-139684 refers to mixed
metal oxide catalysts prepared through the decomposition of a
combination of acetates.
Japanese patent publication no. Sho 54/1979-112793 refers to mixed
metal oxide catalysts prepared using coprecipitated Fe.sub.2
O.sub.3 /Al.sub.2 O.sub.3 on which a catalytically active metal is
supported.
Japanese patent publication no. Sho 63/1988-252908 refers to
ultra-fine gold particles which are supported by a metal oxide,
prepared by the reduction of a gold salt in the presence of the
metal oxide, a procedure commonly used to prepare metal catalysts
supported on metal oxides.
These previous attempts differ from the methods of the present
invention in that they use coprecipitation to prepare the
catalysts, not sequential precipitation. As a result, the catalysts
produced do not have the chemical properties of the catalysts of
the present invention and, accordingly, do not have all of the
advantages of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 represents the extent of CO oxidation with respect to
temperature for one embodiment of a layered mixed oxide catalyst of
this invention.
FIG. 2 represents the extent of CO oxidation with respect to
temperature for another embodiment of a layered mixed oxide
catalyst of this invention .
SUMMARY OF THE INVENTION
It is an object of this invention to provide catalysts for the
conversion of carbon monoxide to a benign substance.
It is also an object of this invention to provide catalysts that
are active at room temperature as well as at the temperatures
reached in a combusting carbonaceous heat source.
It is a further object of this invention to provide catalysts that
oxidize virtually all carbon monoxide produced upon combustion of a
carbonaceous heat source.
It is yet a further object of this invention to provide a method
for producing a layered metal oxide catalyst.
It is also an object of this invention to provide methods for
producing layered metal oxide catalysts, both supported and
unsupported, which allow for control of end-product
composition.
In accordance with this invention, there is provided improved
methods for making metal oxide catalysts which are particularly
useful in a smoking article. The catalysts made by the methods of
this invention comprise transition metal oxide catalysts having a
plurality of metal oxide layers.
The catalysts of this invention are prepared by layering different
metal oxides, one upon the other. It was discovered that the
sequential precipitation of metal oxides, one upon the other,
provides several advantages over prior coprecipitation methods. In
coprecipitated oxides, both materials are uniformly distributed
throughout the surface and the amount of catalytically active
material on the surface is not easily determined or regulated. When
sequential precipitation is used, the metal oxide that is
precipitated last is present only on the surface and therefore its
quantity can be determined and regulated. Furthermore, the
sequential layering of the metal oxide precursor layers during
preparation permits the formation of the required finely divided
outer layer of metal oxide on the surface of the catalyst and
facilitates the interaction between the metal oxides needed to
provide a synergistic effect in the catalytic process.
The metal oxides can also be placed on a "support," an inert
material that does not enter the carbon monoxide conversion
reaction, but rather facilitates that reaction by enhancing the
sites at which those reactions take place.
In another embodiment of this invention, noble metals, or mixtures
thereof, are layered on the mixed transition metal oxide catalysts.
These catalysts may also be placed on a support. Any noble metal
may be used to make the catalysts of this invention, although
considerations such as cost and availability typically enter into
the decision as to which noble metal to use.
Noble metals are generally active over a wide range of temperatures
and are known to have high activities at low temperatures. Noble
metals, however, are also known to have low resistance to toxic
compounds, such as lead and sulfur compounds, and are subject to
sintering at high temperatures, which impair their effectiveness.
Metal oxide catalysts have greater resistance to toxic compounds,
but display reduced activity when used alone at lower
temperatures.
The catalysts of this invention overcome these disadvantages
inherent in noble metal and metal oxide catalysts previously used
in carbon monoxide conversion. It was discovered that by layering
different metal oxides, the resultant mixed metal oxide catalysts
display increased activity at reduced temperatures. When noble
metals are added to the metal oxide catalysts, the noble metal is
layered onto the layered metal oxide structure. This catalyst takes
advantage of the desirable characteristics of the noble metal,
while at the same time the presence of the mixed metal oxides
reduces the undesirable sintering effects usually seen with noble
metals.
The catalysts of this invention undergo surprisingly active
oxidation reactions at relatively low temperatures, i.e., between
about 30.degree. C. and about 40.degree. C. As the temperature
increases, i.e., to between about 90.degree. C. and about
100.degree. C., carbon monoxide is oxidized more rapidly to a
benign substance. As used herein, a "benign substance" may include
carbon dioxide, carbonate, and carbon.
A particular advantage of these catalysts is that when used in
smoking articles they provide a significant level of oxidation of
carbon monoxide but very low adsorption of desirable ingredients
which provide the desirable flavor of the smoke.
According to one embodiment of this invention, the layered mixed
transition metal oxide catalyst is produced by combining a solution
of a metal oxide salt with an aqueous solution of a base to form a
metal hydroxide. An aqueous solution of a salt of a second metal is
then added to the suspension of the metal hydroxide forming a
second layer of the metal hydroxide on the particles of the first
metal hydroxide in the aqueous suspension. The resulting
precipitate is then collected and heated to dehydrate each of the
metal hydroxides of the suspension to produce a mixed metal oxide,
which has one metal oxide layered on a core of a different metal
oxide. This method can be modified to include as a first step the
addition of an aqueous solution of the first metal oxide salt to a
suspension of a support in aqueous base to produce a metal
hydroxide layered on the support. The addition of an aqueous
solution of a salt of a second metal produces a second metal
hydroxide layer on the first metal hydroxide layer. After
separation and heating, this method produces a two-layered mixed
metal oxide on the support.
According to another embodiment of this invention, following the
formation of the layered metal hydroxides as described above, an
aqueous solution of formaldehyde is added to the suspension,
followed by the addition of an aqueous solution of an acid or salt
of a noble metal. This product is then heated to dehydrate each of
the metal hydroxides and to reduce the noble metal salt or acid of
the suspension to produce a noble metal layered upon a layered
mixed metal hydroxide. As with the first embodiment, this method
can be modified to include as a first step the addition of an
aqueous solution of the first metal oxide salt to a suspension of a
support in an aqueous solution of the base. After continuation of
the procedure as described above, this method produces a noble
metal layered on a layered mixed metal oxide on a support.
While the catalysts of this invention are particularly useful for
the catalytic conversion of carbon monoxide emitted from smoking
devices, it is to be understood that the catalysts are also useful
for the catalytic conversion of carbon monoxide in other
applications, including devices used for the conversion of carbon
monoxide from carbonaceous heat sources such as automobile exhaust
conversion devices and indoor air purifiers.
DETAILED DESCRIPTION OF THE INVENTION
The metal oxides of the invention may be formed from the salt of
any metal that is capable of being converted to a metal oxide
having catalytic properties. Preferably, the metal salt is selected
from the group consisting of the nitrates or chlorides of titanium,
chromium, iron, cobalt, nickel, copper, zinc, molybdenum, tungsten,
and tin. More preferred metal salts are cobalt(II)nitrate having
the formula Co(NO.sub.3).sub.2.6H.sub.2 O and iron(III)nitrate
having the formula Fe(NO.sub.3).sub.3.9H.sub.2 O. The most
preferred embodiments consist of the salt of the first metal oxide
being either cobalt(II)nitrate or iron(III)nitrate.
The metal salt is first combined with a base which produces the
desired result of converting the metal nitrate or chloride to an
insoluble metal hydroxide. Any number of bases may be used that are
suitable for this purpose. Preferred bases include an alkali metal
hydroxide, carbonate or bicarbonate, and urea or ammonia. More
preferred bases contain an alkali or alkaline earth metal cation
and an anion selected from the group consisting of hydroxides and
bicarbonates, and include sodium bicarbonate, sodium hydroxide,
potassium carbonate, and lithium hydroxide. Most preferably, the
base is sodium carbonate.
The combining of the metal salt and the base can be accomplished
using one of two methods. Either the aqueous solution of the metal
salt can be added to the solution of the base, or the solution of
the base can be added to the aqueous solution of the metal salt. In
combining the metal salt and the base, a sufficient amount of the
base should be present to convert all of the metal salt to a metal
hydroxide.
Prior to the addition of the second metal salt to produce the
second metal hydroxide, the first metal hydroxide may be separated,
purified, and possibly heated and calcined. The resulting material
can then be placed in a solution of aqueous base and the
preparation procedure continued by the addition of the solution of
the second metal salt.
Following the formation of the metal hydroxide from the reaction of
the metal salt and the base, a solution of a second metal salt is
added. This metal salt should also be a salt of a metal that is
capable of being converted to a metal oxide having catalytic
properties. Preferably, the second metal salt is selected from the
group consisting of the nitrates and chlorides of titanium,
chromium, iron, cobalt, nickel, copper, zinc, molybdenum, tungsten,
and tin. A more preferred metal salt is tin chloride having the
formula SnCl.sub.2. In the most preferred embodiments, where the
salt of the first metal oxide is cobalt(II)nitrate the salt of the
second metal oxide is tin(II)chloride, and where the salt of the
first metal oxide is iron(III)nitrate the salt of the second metal
oxide is selected from the group consisting of cobalt(II)nitrate
and tin(II)chloride.
In combining the second metal salt and the metal hydroxide, a
sufficient amount of the metal salt should be added to yield a
suitable second layer of metal oxide. Preferably, the ratio of the
metal salt to the metal hydroxide should range from about 1:50 to
about 1:4, and, more preferably, from about 2:50 to about 1:10.
To produce a layered mixed metal oxide which is on a support, the
base solution that is combined with the first metal salt may be
first combined with a suspension of a support material. The base
can be combined with the support suspension in a solvent.
The preferred solvent for these procedures is water. However, the
use of other solvents, particularly aqueous mixtures, is not
precluded. The primary criteria for the selection of the solvent is
its capability to dissolve both metal salts and the base and yet
not dissolve the metal hydroxides produced.
Any number of support materials are suitable as a support for the
catalyst. The choice of an effective support for the present
invention depends upon the intended use of the catalyst. Useful
supports for catalysts used in smoking devices include ceramics and
zeolites. Preferred ceramics include ceramics of alumina and
titania. Preferred zeolites include any of a variety of man-made
and naturally occurring crystalline aluminosilicates having a small
enough pore structure to allow for the passage of carbon monoxide
but not the larger molecules present in gas phase cigarette smoke.
Preferred pore sizes may range from about 3 .ANG. to about 20
.ANG.. More preferred pore sizes range from about 5 .ANG. to about
13 .ANG..
Other support materials, e.g., other insulator oxides and
semiconductor oxides, porous carbon or a metal mesh, foam, or
pellet, are useful for catalysts in such applications as automobile
exhaust conversion devices and indoor air purifiers. Porous paper
is also a suitable support material.
An additional layer of a noble metal, or mixture of two noble
metals, may be added upon the layered metal oxide catalyst of this
invention. Preferred noble metals of the invention include any of
the group VIII and Ib noble metal, alone or in combination with a
different noble metal, specifically gold, silver, platinum,
palladium, rhodium, ruthenium, and iridium, and mixtures thereof.
More preferred noble metals are gold, platinum, and palladium.
In combining the metal oxide and the noble metal, sufficient amount
of the noble metal should be added to yield a suitable layer of the
noble metal. Preferably, the noble metal should range up to about
5.0% by weight of the layered metal hydroxide mixture, and, more
preferably, between about 0.1% and about 1.0% by weight of the
layered metal hydroxide mixture.
The mixed hydroxides are then separated by any known method
including filtration or centrifugation. Following this separation
step, the precipitate is washed thoroughly. It is believed that the
washing operation removes soluble salts and other impurities from
the catalyst, which may hinder the activity of the catalyst. While
water is an acceptable washing agent because of its low cost and
availability, and deionized water is preferred, other suitable
solvents may be employed. The catalyst may be washed by contacting
the catalyst with the solvent by known techniques, e.g., passing
the solvent through a column containing the catalyst. The washing
time may vary widely, up t o about 12 hours, and preferably up to
about 2 hours. Ambient temperature is suitable for the washing
step, although higher or lower temperatures may be employed.
The resulting precipitate is then heated to dehydrate the layered
metal hydroxide to form the layered metal oxide catalyst. The
heating step is generally carried out in an inert or oxidizing
(i.e., calcining) atmosphere, preferably in a free oxygen
containing gas atmosphere, such as air. Preferably, the reaction
takes place at a temperature between about 95.degree. C. and about
500.degree. C., more preferably, between about 300.degree. C. and
about 400.degree. C. The heat may be applied uniformly throughout
the heating step or may be gradually increased until the
appropriate reaction temperature is reached. This heating procedure
is generally carried out for between 1 hour and 12 hours so as to
calcine the hydroxide.
EXAMPLE 1
SnO.sub.2 Co.sub.3 O.sub.4
We prepared a layered mixed metal oxide catalyst consisting of tin
oxide (SnO.sub.2) layered over cobalt(II,III)oxide (Co.sub.3
O.sub.4), using a sequential precipitation method. In this method,
we added 10 ml of an aqueous solution of 6.75 grams of
cobalt(II)nitrate Co(NO.sub.3).sub.2.6H.sub.2 O dropwise to 30 ml
of an aqueous solution of 2 molar Na.sub.2 CO.sub.3 under vigorous
stirring conditions. This suspension was stirred vigorously for
one-half hour, yielding a cobalt hydroxide (Co(OH).sub.2)
precipitate. To this suspension, we added dropwise 10 ml of an
aqueous solution of tin(II)chloride (SnCl.sub.2), in varying
concentrations given below for different experimental runs, under
vigorous stirring conditions. This suspension was then stirred for
one hour and the precipitate containing tin hydroxide
(Sn(OH).sub.2) layered on cobalt hydroxide (Co(OH).sub.2) was
separated, washed and centrifuged several times until an absence of
detectable quantities of Cl.sup.- was found. We dried the resulting
precipitate for 12 hours at 95.degree. C. and then calcined it at
380.degree. C. for 4 hours. This calcination procedure yielded a
solid catalyst comprising SnO.sub.2 layered over a Co.sub.3 O.sub.4
core.
We prepared this catalyst using this method over a range of
different concentrations of the SnCl.sub.2 solution. The weight of
SnCl.sub.2 added was varied from 0.0 grams to 0.862 grams. Using
this method, the temperature at which a level of 50% conversion of
CO was reached (T.sub.50 .degree. C.) was examined to determine the
optimum level of SnCl.sub.2 concentration. The results are given in
the following table:
______________________________________ SnCl.sub.2
Co(NO.sub.3).sub.2 % Sn (gms) (gms) T.sub.50 .degree. C.
______________________________________ 15 0.862 6.75 48 10 0.575
6.75 49 8 0.455 6.75 49 6 0.334 6.75 119 4 0.220 6.75 68 2 0.110
6.75 139 1 0.050 6.75 139 0 0.000 6.75 161
______________________________________
This table shows that the preferred concentration of SnCl.sub.2 for
catalytic conversion of CO was 0.445 grams. The overall temperature
ranges through which the percentage conversion of carbon monoxide
is from 0.0% to 100% for the catalysts prepared in this method are
shown in FIG. 1.
EXAMPLE 2
SnO.sub.2 Co.sub.3 O.sub.4
We repeated the general procedure of example 1, with the exception
that in the first step of the process we added the solution of the
base, 2 molar Na.sub.2 CO.sub.3, under vigorous stirring conditions
to an aqueous solution of 6.75 grams of Co(NO.sub.3).sub.2.6H.sub.2
O until a pH of between 8.5 and 9 was obtained. As in example 1, a
10 ml aqueous solution of SnCl.sub.2, in varying concentrations
given below for different experimental runs, was then added under
vigorous stirring conditions. The resulting precipitate, comprising
Sn(OH).sub.2 layered over Co(OH).sub.2, was then separated, washed,
dried, and calcined using the procedures described in example
1.
We prepared the catalyst using this method over a range of
different concentrations of the SnCl.sub.2 suspension. The weight
of SnCl.sub.2 added was varied from 0.0 grams to 0.862 grams. Using
this method, the temperature at which a level of 50% conversion of
CO was reached (T.sub.50 .degree. C.) was examined to determine the
optimum level of SnCl.sub.2 concentration. The results are given in
the following table:
______________________________________ SnCl.sub.2
Co(NO.sub.3).sub.2 % Sn (gms) (gms) T.sub.50 .degree. C.
______________________________________ 15 0.862 6.75 126 10 0.575
6.75 105 8 0.455 6.75 89 6 0.334 6.75 62 4 0.220 6.75 58 2 0.110
6.75 105 1 0.050 6.75 126 0 0.000 6.75 --
______________________________________
This table shows that the preferred concentration of SnCl.sub.2 for
catalytic conversion of CO was between 0.220 grams and 0.334 grams.
The overall temperature ranges through which the percentage
conversion of carbon monoxide is from 0.0% to 100% for the
catalysts prepared in this method are shown in FIG. 2.
EXAMPLE 3
Au/1SnO.sub.2 Co.sub.3 O.sub.4 SiO.sub.2
We prepared a layered mixed metal oxide catalyst consisting of gold
layered on a second metal oxide, SnO.sub.2, layered on a first
metal oxide, Co.sub.3 O.sub.4, which was layered on a support of
silicon oxide (SiO.sub.2). In this procedure, we added dropwise 40
ml of an aqueous solution consisting of 5.25 grams of
Co(NO.sub.3).sub.2.6H.sub.2 O to 70 ml of an aqueous suspension
containing 15.0 grams of SiO.sub.2 (Davison, grade 56) and 2 molar
Na.sub.2 CO.sub.3, under vigorous stirring conditions. To this
suspension was added 10 ml of an aqueous solution of 0.0452 grams
of SnCl.sub.2, also under vigorous stirring conditions. To this
suspension was added 0.5 ml of an aqueous solution of 37%
formaldehyde (HCHO). To this suspension was added 10 ml of an
aqueous solution of chloroauric acid (HAuCl.sub.4) at a rate of 2
ml per minute. The resulting suspension was then stirred for two
hours and the resulting precipitate was separated, washed and
centrifuged several times until an absence of detectable quantities
of Cl.sup.- was found. We dried the resulting precipitate for 12
hours at 95.degree. C. and then calcined it at 380.degree. C. for 4
hours. This calcination procedure yielded a solid catalyst
comprising gold layered on SnO.sub.2, layered on Co.sub.3 O.sub.4,
which was layered over a core of SiO.sub.2 support. Using this
method, we found that T.sub.50 .degree. C. was reached at
140.degree. C. using the preferred concentration by atomic weight
comprising 2% Au, 1.2% SnO.sub.2 and 7.4% Co.sub.3 O.sub.4.
EXAMPLE 4
Au/2SnO.sub.2 Co.sub.3 O.sub.4 SiO.sub.2
We repeated the procedure of example 3, with the exception that in
the second step of the procedure, we added 10 ml of an aqueous
solution containing 0.0904 grams of SnCl.sub.2. This method yielded
a modification of the catalyst of example 3, Au/2SnO.sub.2 Co.sub.3
O.sub.4 SiO.sub.2. Using this procedure, we found that T.sub.50
.degree. C. was reached at 240.degree. C. using the preferred
concentration by atomic weight comprising 1.9% Au, 2.3% SnO.sub.2,
and 6.9% Co.sub.3 O.sub.4.
EXAMPLE 5
Pt/1SnO.sub.2 Co.sub.3 O.sub.4 SiO.sub.2
We prepared a layered mixed metal oxide catalyst consisting of
platinum layered on a second metal oxide, SnO.sub.2, layered on a
first metal oxide, Co.sub.3 O.sub.4, which was layered on an
SiO.sub.2 support. In this method, we added 40 ml of an aqueous
solution of 5.25 grams of Co(NO.sub.3).sub.2.6H.sub.2 O dropwise to
70 ml of an aqueous suspension of 15 grams of SiO.sub.2 (Davison,
grade 56) and 2 molar Na.sub.2 CO.sub.3, under vigorous stirring
conditions. To this suspension was added 10 ml of an aqueous
solution of 0.0452 grams of SnCl.sub.2, also under vigorous
stirring conditions. This suspension was heated to 90.degree. C.,
and then to this suspension was added an aqueous suspension of 10
ml of 0.1036 grams of chloroplatinic acid (H.sub.2
PtCl.sub.6.6H.sub.2 O) at a rate of 1 milliliter per minute. To
this suspension was added 0.5 ml of an aqueous solution of HCHO.
The resulting suspension was kept at the 90.degree. C. temperature
for one hour. The resulting suspension was then stirred for two
hours and the precipitate was separated, washed and centrifuged
several times until an absence of detectable quantities of Cl.sup.-
was found. We dried the resulting precipitate for 12 hours at
95.degree. C. and then calcined at 380.degree. C. for 4 hours. This
calcination procedure yielded a solid catalyst comprising platinum
layered on SnO.sub.2, layered on Co.sub.3 O.sub.4, layered over an
SiO.sub.2 support. Using this procedure, we found that T.sub.50
.degree. C. was reached at 196.degree. C. using the preferred
concentration by atomic weight of 2.1% Pt, 1.2% SnO.sub.2, and 7.6%
Co.sub.3 O.sub.4.
EXAMPLE 6
Pt/2SnO.sub.2 Co.sub.3 O.sub.4 SiO.sub.2
We repeated the procedure of example 5, with the exception that the
10 ml aqueous solution of SnCl.sub.2 contained 0.0904 grams of
SnCl.sub.2, and the HCHO solution was not added. This amended
procedure yielded a modification of the catalyst of example 5,
platinum layered 2SnO.sub.2 layered on Co.sub.3 O.sub.4, on a
catalyst support of SiO.sub.2. Using this procedure, we found that
T.sub.50 .degree. C. was reached at 205.degree. C. using the
preferred concentration by atomic weight of 2% Pt, 2.3% SnO.sub.2
and 6.8% Co.sub.3 O.sub.4.
EXAMPLE 7
Pd/1SnO.sub.2 Co.sub.3 O.sub.4 SiO.sub.2
We prepared a layered mixed metal oxide catalyst consisting of
palladium layered on a second metal oxide, SnO.sub.2, layered on a
first metal oxide, Co.sub.3 O.sub.4, which was layered on an
SiO.sub.2 support. In this method, we added 40 ml of an aqueous
solution of 5.25 grams of Co(NO.sub.3).sub.2.6H.sub.2 O dropwise to
a 70 ml aqueous suspension of 15 grams of SiO.sub.2 (Davison, grade
56) and 2 molar Na.sub.2 CO.sub.3, under vigorous stirring
conditions. To this suspension was added 10 ml of an aqueous
solution of 0.0452 grams of SnCl.sub.2, also under vigorous
stirring conditions. This suspension was heated to 90.degree. C.,
and then to this suspension was added an aqueous solution of 10 ml
of 0.0589 grams of sodium chloropallidate (Na.sub.2 PdCl.sub.4) at
a rate of 1 milliliter per minute. To this suspension was added
0.05 ml of an aqueous solution of HCHO. The resulting suspension
was kept at the 90.degree. C. temperature for 10 minutes. The
resulting suspension was then stirred for two hours and the
precipitate was separated, washed and centrifuged several times
until an absence of detectable quantities of Cl.sup.- was found. We
dried the resulting precipitate for 12 hours at 95.degree. C. and
then calcined it at 380.degree. C. for 4 hours. This calcination
procedure yielded a solid catalyst comprising palladium layered on
the SnO.sub.2, layered on Co.sub.3 O.sub.4, layered over an
SiO.sub.2 support. Using this procedure, we found that T.sub.50
.degree. C. was reached at 144.degree. C. using the preferred
concentration by atomic weight comprising 1.1% pd, 1.2% SnO.sub.2
and 7.6% Co.sub.3 O.sub.4.
EXAMPLE 8
Pd/2SnO.sub.2 Co.sub.3 O.sub.4 SiO.sub.2
We repeated the procedure of example 7, with the exception that the
10 ml aqueous solution of SnCl.sub.2 contained 0.0904 grams of
SnCl.sub.2. This amended procedure yielded a modification of the
catalyst of example 7, palladium layered on 2SnO.sub.2 layered on
Co.sub.3 O.sub.4, on an SiO.sub.2 support. Using this procedure, we
found that T.sub.50 .degree. C. was reached at 161.degree. C. using
the preferred concentration by atomic weight comprising 1.1% Pd,
2.3% SnO.sub.2, and 6.4% Co.sub.3 O.sub.4.
EXAMPLE 9
AuPd/SnO.sub.2 Co.sub.3 O.sub.4
We prepared a layered mixed metal oxide catalyst consisting of a
mixture of gold and palladium layered on a second metal oxide,
SnO.sub.2, layered on a first metal oxide, Co.sub.3 O.sub.4. In
this method, we added 15 ml of an aqueous solution of 6.75 grams of
Co(NO.sub.3).sub.2.6H.sub.2 O dropwise under vigorous stirring
conditions to a 40 ml aqueous solution containing 2 molar Na.sub.2
CO.sub.3. To this suspension was added 10 ml of an aqueous solution
of 0.0862 grams of SnCl.sub.2, also under vigorous stirring
conditions. To this suspension was added an aqueous solution of 15
ml of a combined solution of 0.031 grams of palladium nitrate
(Pd(NO.sub.3).sub.2) and 0.053 grams of chloroauric acid
(HAuCl.sub.4). The resulting suspension was then stirred for two
hours and the precipitate was separated, washed and centrifuged
several times until an absence of detectable quantities of Cl.sup.-
was found. We dried the resulting precipitate for 12 hours at 95
.degree. C. and then calcined at 380.degree. C. for 4 hours. This
calcination procedure yielded a solid catalyst comprising a mixture
of 0.5% gold and 0.5% palladium layered on SnO.sub.2, layered on
Co.sub.3 O.sub.4.
We prepared the catalyst using this procedure over a range of
different concentrations of Au and Pd. The results are given in the
following table:
______________________________________ % Au % Pd % SnO.sub.2 %
Co.sub.3 O.sub.4 T.sub.50 .degree. C.
______________________________________ 1.0 0.0 15.0 84.0 46 0.8 0.2
15.0 84.0 75 0.6 0.4 15.0 84.0 131 0.5 0.5 15.0 84.0 128 0.4 0.6
15.0 84.0 109 0.2 0.8 15.0 84.0 114 0.0 1.0 15.0 84.0 68
______________________________________
EXAMPLE 10
PtRh/CuOCo.sub.3 O.sub.4
We prepared a layered mixed metal oxide catalyst consisting of a
mixture of platinum and rhodium layered on a second metal oxide,
copper oxide (CuO), layered on a first metal oxide, Co.sub.3
O.sub.4. In this procedure, we added dropwise 15 ml of an aqueous
solution consisting of 6.75 grams of Co(NO.sub.3).sub.2.2H.sub.2 O
to 35 ml of an aqueous solution of 2 molar Na.sub.2 CO.sub.3, under
vigorous stirring conditions. To this suspension was added 10 ml of
an aqueous solution of 0.534 grams of copper nitrate
(Cu(NO.sub.3).sub.2), also under vigorous stirring conditions. This
suspension was stirred for one half hour. To this suspension was
then added an aqueous solution of 10 ml of a combined solution of
0.066 grams of chloroplatinic acid (H.sub.2 PtCl.sub.6.6H.sub.2 O)
and 0.033 grams of rhodium chloride (RhCl.sub.3). The suspension
was then heated to 80.degree. C. and 1 ml of HCHO was added. The
resulting suspension was then stirred for one hour, after which the
precipitate was separated, washed and centrifuged several times
until an absence of detectable quantities of Cl.sup.- was found. We
dried the resulting precipitate for 12 hours at 95.degree. C. and
then calcined it at 380.degree. C. for 4 hours. This calcination
procedure yielded a solid catalyst comprising a mixture of 0.5%
platinum and 0.5% rhodium layered on CuO, layered on Co.sub.3
O.sub.4.
We prepared the catalyst using this procedure over a range of
different concentrations of Pt and Rh. The results are given in the
following table:
______________________________________ % Pt % Rh % CuO % Co.sub.3
O.sub.4 T.sub.50 .degree. C. ______________________________________
1.0 0.0 9.0 90.0 81 0.8 0.2 9.0 90.0 71 0.6 0.4 9.0 90.0 81 0.5 0.5
9.0 90.0 90 0.4 0.6 9.0 90.0 97 0.2 0.8 9.0 90.0 90 0.0 1.0 9.0
90.0 81 ______________________________________
* * * * *